Unusual Executable File Creation by a System Critical Process

  1[metadata]
  2creation_date = "2020/08/19"
  3integration = ["endpoint", "windows", "m365_defender", "sentinel_one_cloud_funnel"]
  4maturity = "production"
  5updated_date = "2025/03/20"
  6
  7[transform]
  8[[transform.osquery]]
  9label = "Osquery - Retrieve DNS Cache"
 10query = "SELECT * FROM dns_cache"
 11
 12[[transform.osquery]]
 13label = "Osquery - Retrieve All Services"
 14query = "SELECT description, display_name, name, path, pid, service_type, start_type, status, user_account FROM services"
 15
 16[[transform.osquery]]
 17label = "Osquery - Retrieve Services Running on User Accounts"
 18query = """
 19SELECT description, display_name, name, path, pid, service_type, start_type, status, user_account FROM services WHERE
 20NOT (user_account LIKE '%LocalSystem' OR user_account LIKE '%LocalService' OR user_account LIKE '%NetworkService' OR
 21user_account == null)
 22"""
 23
 24[[transform.osquery]]
 25label = "Osquery - Retrieve Service Unsigned Executables with Virustotal Link"
 26query = """
 27SELECT concat('https://www.virustotal.com/gui/file/', sha1) AS VtLink, name, description, start_type, status, pid,
 28services.path FROM services JOIN authenticode ON services.path = authenticode.path OR services.module_path =
 29authenticode.path JOIN hash ON services.path = hash.path WHERE authenticode.result != 'trusted'
 30"""
 31
 32
 33[rule]
 34author = ["Elastic"]
 35description = """
 36Identifies an unexpected executable file being created or modified by a Windows system critical process, which may
 37indicate activity related to remote code execution or other forms of exploitation.
 38"""
 39from = "now-9m"
 40index = [
 41    "winlogbeat-*",
 42    "logs-endpoint.events.file-*",
 43    "logs-windows.sysmon_operational-*",
 44    "endgame-*",
 45    "logs-m365_defender.event-*",
 46    "logs-sentinel_one_cloud_funnel.*",
 47]
 48language = "eql"
 49license = "Elastic License v2"
 50name = "Unusual Executable File Creation by a System Critical Process"
 51note = """## Triage and analysis
 52
 53### Investigating Unusual Executable File Creation by a System Critical Process
 54
 55Windows internal/system processes have some characteristics that can be used to spot suspicious activities. One of these characteristics is file operations.
 56
 57This rule looks for the creation of executable files done by system-critical processes. This can indicate the exploitation of a vulnerability or a malicious process masquerading as a system-critical process.
 58
 59> **Note**:
 60> This investigation guide uses the [Osquery Markdown Plugin](https://www.elastic.co/guide/en/security/current/invest-guide-run-osquery.html) introduced in Elastic Stack version 8.5.0. Older Elastic Stack versions will display unrendered Markdown in this guide.
 61
 62#### Possible investigation steps
 63
 64- Investigate the process execution chain (parent process tree) for unknown processes. Examine their executable files for prevalence, whether they are located in expected locations, and if they are signed with valid digital signatures.
 65- Investigate other alerts associated with the user/host during the past 48 hours.
 66- Investigate any abnormal behavior by the subject process such as network connections, registry or file modifications, and any spawned child processes.
 67- Examine the host for derived artifacts that indicate suspicious activities:
 68  - Analyze the process executable using a private sandboxed analysis system.
 69  - Observe and collect information about the following activities in both the sandbox and the alert subject host:
 70    - Attempts to contact external domains and addresses.
 71      - Use the Elastic Defend network events to determine domains and addresses contacted by the subject process by filtering by the process' `process.entity_id`.
 72      - Examine the DNS cache for suspicious or anomalous entries.
 73        - $osquery_0
 74    - Use the Elastic Defend registry events to examine registry keys accessed, modified, or created by the related processes in the process tree.
 75    - Examine the host services for suspicious or anomalous entries.
 76      - $osquery_1
 77      - $osquery_2
 78      - $osquery_3
 79  - Retrieve the files' SHA-256 hash values using the PowerShell `Get-FileHash` cmdlet and search for the existence and reputation of the hashes in resources like VirusTotal, Hybrid-Analysis, CISCO Talos, Any.run, etc.
 80- Investigate potentially compromised accounts. Analysts can do this by searching for login events (for example, 4624) to the target host after the registry modification.
 81
 82
 83### False positive analysis
 84
 85- This activity is unlikely to happen legitimately. Benign true positives (B-TPs) can be added as exceptions if necessary.
 86
 87### Response and remediation
 88
 89- Initiate the incident response process based on the outcome of the triage.
 90- Isolate the involved host to prevent further post-compromise behavior.
 91- If the triage identified malware, search the environment for additional compromised hosts.
 92  - Implement temporary network rules, procedures, and segmentation to contain the malware.
 93  - Stop suspicious processes.
 94  - Immediately block the identified indicators of compromise (IoCs).
 95  - Inspect the affected systems for additional malware backdoors like reverse shells, reverse proxies, or droppers that attackers could use to reinfect the system.
 96- Remove and block malicious artifacts identified during triage.
 97- Run a full antimalware scan. This may reveal additional artifacts left in the system, persistence mechanisms, and malware components.
 98- Determine the initial vector abused by the attacker and take action to prevent reinfection through the same vector.
 99- Using the incident response data, update logging and audit policies to improve the mean time to detect (MTTD) and the mean time to respond (MTTR).
100"""
101risk_score = 73
102rule_id = "e94262f2-c1e9-4d3f-a907-aeab16712e1a"
103severity = "high"
104tags = [
105    "Domain: Endpoint",
106    "OS: Windows",
107    "Use Case: Threat Detection",
108    "Tactic: Defense Evasion",
109    "Tactic: Execution",
110    "Resources: Investigation Guide",
111    "Data Source: Elastic Endgame",
112    "Data Source: Elastic Defend",
113    "Data Source: Sysmon",
114    "Data Source: Microsoft Defender for Endpoint",
115    "Data Source: SentinelOne",
116]
117timestamp_override = "event.ingested"
118type = "eql"
119
120query = '''
121file where host.os.type == "windows" and event.type != "deletion" and
122  file.extension : ("exe", "dll") and
123  process.name : ("smss.exe",
124                  "autochk.exe",
125                  "csrss.exe",
126                  "wininit.exe",
127                  "services.exe",
128                  "lsass.exe",
129                  "winlogon.exe",
130                  "userinit.exe",
131                  "LogonUI.exe")
132'''
133
134
135[[rule.threat]]
136framework = "MITRE ATT&CK"
137[[rule.threat.technique]]
138id = "T1211"
139name = "Exploitation for Defense Evasion"
140reference = "https://attack.mitre.org/techniques/T1211/"
141
142
143[rule.threat.tactic]
144id = "TA0005"
145name = "Defense Evasion"
146reference = "https://attack.mitre.org/tactics/TA0005/"
147[[rule.threat]]
148framework = "MITRE ATT&CK"
149[[rule.threat.technique]]
150id = "T1203"
151name = "Exploitation for Client Execution"
152reference = "https://attack.mitre.org/techniques/T1203/"
153
154
155[rule.threat.tactic]
156id = "TA0002"
157name = "Execution"
158reference = "https://attack.mitre.org/tactics/TA0002/"